For electrode materials of the lithium secondary batteries, oxides of lithium-containing transition metals are used, and in particular, composite materials of lithium cobaltate (LiCoO2) and carbon (C) are used. These composite materials can be synthesized relatively easily. As other electrode materials (or positive electrode materials) of the lithium secondary batteries, for example, LiNiO2, LiCoxNi(1-x)O2 (x=1˜0), LiMn2O4 and the like can be mentioned.
As described above, since the electrode materials (or positive electrode materials) of the lithium secondary batteries contain rare and valuable substances, such as cobalt compounds, lithium compounds and/or the like, it is desired to recover such valuable substances from used lithium secondary batteries. Namely, the recovered valuable substances can be recycled and used again, for example, as the electrode materials for the lithium secondary batteries.
In the past, recycling of the positive electrode materials generally employs a wet process, in order to recover the cobalt compounds and the like, through several steps of processing oxides.
For example, in the recovery method for the valuable metals described in JP 10-287864 A, an eluate is separated by adding mineral acid, such as hydrochloric add or sulfuric acid, or a mixture of the mineral acid and aqueous hydrogen peroxide to active materials used for the positive electrode of the lithium secondary battery. Thereafter, the resultant eluate is extracted and separated into desired components by contacting it with a solvent containing a special metal extractant, such as bis(1,1,3,3-tetramethylbutyl)phosphinic add compounds and the like, and a solvent phase of the so-obtained extract is then contacted with the mineral acid for back extraction and separation, thereby recovering the valuable metals.
As described above, the steps of processing oxides in the conventional recovery method for the valuable metals include multi-stage steps, such as acid dissolution, solvent extraction, precipitation, acid treatment, heat treatment and the like, as such requiring relatively complex and large-sized processing equipment as well as a higher processing temperature and a longer processing time.
In fact, in the case of recovering cobalt (Co) that is one of the valuable metals from the lithium secondary battery by using the equipment employing the wet process (or aqueous process), a large-sized plant and higher production cost should be required. Therefore, it is necessary for commercial profit to process a quite great amount of lithium secondary batteries. Currently, Co is a by-product of nickel (Ni), and is collected, as such a by-product, by mixing Ni ore, which is usually employed as a main raw material, with disposed lithium secondary batteries and then processing the mixture by utilizing existent equipment for refining (or collecting) Ni and Co from the Ni ore. Thus, it has not been considered so far commercially practical to operate such wet process equipment in order to process only the disposed lithium secondary batteries as the main raw material.
In the recovery method for recovering the valuable metals from the used lithium secondary batteries, described in JP 10-158751 A, the used lithium secondary batteries are first calcinated, and then reduced with carbon, so as to be brought into a state likely to be changed into metal condensate, such as cobalt metal powder particles, nickel metal powder particles or the like. Thereafter, the calcinated material is ground, screened, and separated into a part rich in the valuable metals and a part containing a lower content of the valuable metals. Subsequently, the condensate of the valuable metals is mixed with a calcium compound, and the resultant mixture is heated and melted at 1500° C. or higher temperature, so as to cause aluminum components to be incorporated and removed into slag of the calcium compound. In this way, the valuable metals, such as cobalt, nickel and the like, can be recovered.
However, in the conventional recovery method described above, it is quite difficult to effectively collect lithium that is one of the valuable metals. In addition, in the case of processing the electrode material in which other rare and valuable components are also contained, there is a need for employing separate processing methods respectively suitable for collecting such metal components.
To address such problems of the conventional recovery methods, JP 2005-11698 A, filed by applicants including the applicant of the current application as one of the co-applicants thereof, discloses a method and an apparatus for recycling the electrode materials of the lithium secondary batteries, in which a recycling process can be performed, with simpler steps and in a shorter time, as compared with the conventional methods as previously known. According to this recycling method and apparatus, the recovery or collection of lithium can be performed more appropriately than the conventional recovery methods in which such recovery was quite difficult.
Specifically, in the recycling method and apparatus described in JP 2005-11698 A, lithium cobaltate (LiCoO2), the positive electrode material of the lithium secondary battery, is subjected to a reducing reaction in molten lithium chloride (LiCl) together with metal lithium (Li) (i.e., in a reducing reaction step). Consequently, lithium oxide (Li2O) is produced, while cobalt oxide (CoO), cobalt (Co) and the like are precipitated and then separated. Thereafter, the lithium oxide (Li2O) is electrolyzed in the molten lithium chloride, and metal lithium (Li) will be deposited onto and collected from a cathode. As described above, the recycling method and apparatus employ a Li—LiCl process as a main process thereof.
One example of components (weight ratios) constituting the lithium secondary battery is shown in FIG. 14. Additionally, one example of an electrode structure of the lithium secondary battery is shown in FIG. 15. A film (or separator), the positive electrode and negative electrode, respectively shown in FIG. 14, correspond together to an electrode portion 40 shown in FIG. 15, and such a sheet of the electrode portion 40 is wound around a core to form each electrode of the battery. As shown in FIG. 15, in the electrode portion 40 of the lithium secondary battery, the positive electrode 41 and the negative electrode 42 are separated from each other by the film 43 as the separator.
The positive electrode 41 is formed by attaching lithium cobaltate (LiCoO2) powder 44 to both faces of an aluminum (Al) foil 45, wherein the LiCoO2 powder 44 is molded together with a fluororesin binder (i.e., polyvinylidene fluoride: PVdF). On the other hand, the negative electrode 42 is formed by attaching carbon black powder 46 to both faces of a copper (Cu) foil 47, wherein the carbon black powder 46 is molded together with a resin binder.
In the recycling method described above, since the Li—LiCl process is employed as the main process, it has been found that, if pre-treatment steps and/or post-treatment steps that have been employed in the conventional wet process are applied to this method, the following various problems will occur.
Namely, if the Al foil used as the electrode material of the lithium secondary battery is incorporated, AlCo alloys and/or other intermetallic compounds will be produced, leading to deterioration of purity of recovered Co. Namely, in the positive electrode of the lithium secondary battery, the lithium cobaltate powder is molded together with the fluororesin binder (i.e., polyvinylidene fluoride: PVdF) and attached to the Al foil. As such, if a heat treatment is provided while the lithium cobaltate powder and the Al foil are contacted with each other, AlCo oxides will be produced and then reduced in the main process (i.e., the Li—LiCl process). Therefore, the AlCo alloys and/or other intermetalic compounds as described above will be produced.
However, in the conventional wet process (or aqueous process), the incorporation of such AlCo alloys or the like will not be problematic because these products can be dissolved in acids employed therein. Instead, the production of the AlCo alloys or the like will be problematic when the molten salt process (i.e., the Li—LiCl process), rather than the aqueous process, is employed as the main process.
In addition, when the fine powder of carbon, one of the materials constituting the negative electrode of the lithium secondary electrode, is incorporated, Li will be wasted because of reaction of the carbon with Li necessary for use in a Li reduction reaction, leading to disadvantage in the cost. This is because oxygen necessary for burning and removing the carbon black will not be sufficiently contacted with the carbon black in an ordinary combustion process, as such the carbon black constituting the negative electrode may tend to remain intact.
Additionally, when the fluororesin binder, one of the electrode materials of the lithium secondary electrode, is incorporated, Li will be wasted because of reaction of the fluororesin with Li for use in the Li reduction reaction, leading to production of lithium fluoride (LiF). Thus, the purity of the recovered Co will be degraded, making it difficult to perform magnetic separation for Co.
The difficulty of the magnetic separation for Co caused by the production of LiF can be described as follows. Namely, when LiF is produced, metal powder, such as Co powder, Cu powder and the like, is incorporated into its matrix. Therefore, it will be difficult to discriminate the Cu powder, Al powder and the like from the Co powder that could be otherwise magnetically separated in nature.
Because the lithium cobaltate powder is molded together with the fluororesin binder (PVdF) in the positive electrode of the lithium secondary battery, oxygen and moisture necessary for decomposing, burning and removing the PVdF will not be sufficiently contacted with the binder binding particles of lithium cobaltate together, in an ordinary combustion process. Therefore, the PVdF cannot be completely removed, thus producing the LiF matrix through the reaction between Li used for the reducing reaction in the main process and F contained in the PVdF.
To address this problem, upon recovering the valuable substances, such as Co, Li and the like, from the lithium secondary battery by using the Li—LiCl process as the main process, it is necessary to remove the Al foil, carbon fine particles and fluroresin binder, as much as possible, in the pre-treatment step prior to the main process.
Additionally, in the case of using the Li—LiCl process as the main process, it should be noted that the molten salt (LiCl) is likely to be associated with and/or attached to the recovered Co. Furthermore, there is a possibility that LiF may be incorporated in the recovered Co.
Accordingly, upon recovering the valuable substances, such as Co, Li and the like, from the lithium secondary battery by using the Li—LiCl process as the main process, it is necessary, for a post-treatment step in succession to the main process, to remove the molten salt (LiCl) that may be associated with and/or attached to the recovered Co, as much as possible, as well as to remove LiF, as much as possible, in order to enhance the purity of the recovered Co.
As the pre-treatment process in the conventional processing method, such as the wet process or the like, which does not employ the Li—LiCl process as the main process, a method of using aqueous inorganic acid (JP 2001-185241 A), a method of using heat separation (JP 10-8150 A), a method of applying thermal impact (JP 10-241750 A), a method of providing heating, crushing and acid dissolution (JP 2003-157913 A, JP 11-97076 A), a method of floating selection (JP 2003-272720 A), a method of providing heating, crushing and halogen gas formation (JP 2005-42189 A, and the like are known. None of these pre-treatment processes can completely solve the problem described above in the case of using the Li—LiCl process as the main process.